The success of plant cultivation is endangered by several diseases and pests (e.g. fungal diseases, insects, mammals etc.). The chewing of seeds and seedlings and the diseases of the growing plant result in serious crop damage. The germinating seeds, the tubers and some leafed plants are the most unprotected and any damage might become fatal. Some further diseases caused by the infection of the seed might appear on the crops (e.g. rust and mildew diseases of cereals).
In order to avoid the above mentioned serious damage and to ensure the foodstuff-demands of the population, seed dressing (also referred to as dressing) has been used for a long time. The essential feature of the said process is that the propagative organs of the plant are contacted with chemical substances (referred to furtheron as plant protecting agents or pesticides) which destroy the pests dwelling on the seed or in the vicinity thereof in the soil. The said plant protecting agents provide healthy seeds on the one hand while on the other they kill the soil dwelling sucking-chewing pests. Other known plant protecting agents are adsorbed by the plant and provide protection to the plant for a shorter or longer period of time.
It is an essential feature of the seed dressing procedure that the propagative material and the plant protecting agent should be in contact for a prolonged period of time and the said contact should be maintained when the propagative material enters the soil.
Nowadays in seed dressing technology additives which promote the adhesion of the fungicide and enhance seed dressing are widespreadly used. The users particularly demand additives which posses high adhesive strength, color intensively, dry rapidly and contain no active ingredient because only such additives are suitable for seed dressing wherein the economy in the use of materials is taken into consideration and the rate of application is adapted to the degree of infection.
The known seed dressing methods are as follows:
(1) Wet seed dressing. The pesticide is suspended or--if possible--dissolved in water. The seeds are soaked in this mixture, thereafter filtered and dried. Thus good contact is made between the pesticide and the seeds but the amount of the active pesticidal ingredient which adheres is often lower than that required for the safe protection of the seeds. Further drawbacks are the complicated character of the process, the high labor demand and the costs of drying. For these reasons the said process is not used in practice any more.
(2) Powder dressing. The object of this method is the elimination of the drawbacks of wet technology. The essence of the process is that the active ingredient is ground to a fine powder and a powdered additive is added which promotes adhesion. The process involves, however, serious difficulties. The powder is namely adhered only to the external surface of the propagating material and generally avoids the germ homozygotes. Therefore in the absence of moisture the substance capable of absorption can penetrate the seeds only after sowing under the effect of the humidity of the soil. The adhesion to the dry seeds is weak and therefore the required amount of active ingredient can be applied only with difficulties. Moreover a great part of the pesticide dusts off during treatment, storage and transport of the seeds, consequently it can not exert the desired effect and constitutes health hazards to the handling staff as well.
(3) Moistened seed dressing. From the active ingredient a suspension is prepared with such an amount of water which can be still absorbed by the seeds without increasing the moisture content during storage over the still allowable limit. The object of this method is to maintain the advantages of the wet and dry technologies with the possible strongest suppression of the drawbacks thereof. This object can be reached, however, only by a certain compromise. It is a particularly serious problem that after drying a significant amount of the plant protecting agent dusts off. Water soluble adhesives are used to promote adhesion. These agents are dissolved in water and form colloids but increase the viscosity of the solution to such a large extent that a very thick, dense suspension is formed even if the said adhesive is used in high dilution. If, on the other hand, a small amount of adhesive is used the desired biological effect cannot be achieved because a significant part of the active ingredient and the pesticide dusts off during storage or sowing.
According to the prior art the following attempts have been made to overcome the above drawbacks and difficulties:
(1) Combined pesticides are put on the market which comprise the active ingredients of the seed dressing agent in a pre-determined ratio admixed in a plastic dispersion (e.g. Evershield, Buvishield products). The active ingredient adheres to the seeds by means of a film forming plastic material. The disadvantage of this process is that the composition of the active ingredients is not adapted to the particular infection to be overcome. Thus on the one hand it is necessary to put on the market compositions adapted at least to the most important cultures whilde one the other hand it causes wasteful consumption because a more effective and expansive agent must be used for the treatment of lower infections too. A further drawback is that the germinating strength is reduced and the seeds stick together.
(2) Seed dressing agents have been elaborated which contain no active ingredient. These are solutions of natural (e.g. pine-resin, shellac) or synthetic resins formed with organic solvents (e.g. alcohol). The solutions are admixed with the suspension of the dressing agent and the mixture is applied onto the seeds. After dressing the thus treated seeds the solvent and the excess of water must be removed by drying. The step of drying is to be carried out under constant moving of the seeds in order to avoid the sticking together thereof. This step is carried out by using special equipment.
Such seed dressing methods are disclosed in European patent specification No. 0,010,630 (shellac is used as binding agent), European patent specification No. 0,013,763 (vermiculite and orillanalate are used as coating agent) and Japanese patent application Kokai No. 2,631,032 (a maltotriase polymer is used as coating agent).